Is Oatmeal a Starch or a Fiber?

Oatmeal makes a nutritious breakfast.

Oatmeal is a healthy grain option, regardless of whether you choose old-fashioned, quick or instant oats, since it is a whole grain and contains almost no sugar. Like most carbohydrate foods, oatmeal comprises some of all three types of carbohydrates -- starch, fiber and sugar -- so it is both a starch- and a fiber-containing food.

Starch

Starch is a type of complex carbohydrate, since it is made up of a number of sugar molecules bound together. Digestive enzymes break these bonds to turn the starch back to sugars during digestion. Starches are found in starchy vegetables like peas, corn and potatoes, as well as in grains and legumes.

Oatmeal Starch Content

Most of oatmeal, about 84 percent by weight, is made up of water. However, starch is the next major component at 12 percent. Each 1-cup serving of cooked oatmeal contains 27.14 grams of starch. This is about 98 percent of the 28.08 grams of carbohydrate in oatmeal. Oatmeal only contains trace amounts of sugar, as well as 2 percent fat and 3 percent protein by weight.

Fiber

Fiber is another type of complex carbohydrate made of at least three sugars combined together. However, people can't make the enzymes to break down fiber, so it passes through the digestive tract basically unchanged. In the process, it provides health benefits. Insoluble fiber helps keep you from getting constipated or experiencing other digestive complaints, while soluble fiber helps you feel full for longer and lowers your blood glucose, since it delays the emptying of the stomach and slows the release of glucose into your bloodstream. It can also help lower your cholesterol, since the gel soluble fiber forms when combined with liquids binds with cholesterol so it isn't all absorbed into your bloodstream.

Oatmeal Fiber Content

Oatmeal consists of about 2 percent fiber. Eating a cup of oatmeal will provide you with 4 grams of fiber, helping you meet your recommended fiber intake of 21 to 38 grams per day. This is about 14 percent of the carbohydrate in oatmeal. About half of this fiber consists of the soluble fiber beta-glucan, the type of fiber that helps lower your cholesterol and your heart disease risk, and the other half consists of insoluble fiber.